The present invention relates to corrugating machines utilized in the manufacture of single faced corrugated paper products, and more particularly to an improved corrugating machine design which significantly reduces particular operating problems prevalent in conventional single facer machines.
Conventional "single facer" corrugating machines have included a pair of fluted rolls of substantial mass supported on bearings at each end (generally termed upper and lower corrugating rolls). The corrugating rolls include elongated intermeshing flutes which cooperate to deform a paper medium passed between them to provide corrugations in the medium. Such conventional machines also include a smooth surface "pressure roll" located adjacent and biased toward the periphery of the lower corrugating roll for applying a paper liner to the adhesively treated tips of the corrugated medium to yield a single faced product.
One problem encountered with such conventional machines relates to their adaptability to different operating conditions. In order to provide a more even corrugating force (nip pressure) across the width of such machines, the upper corrugating roll is generally crowned. The manufacture of a crowned roll shape is an expensive and time-consuming process, and changing rolls can be a similarly time-consuming and expensive process. Thus, the selection of roll crowns and related nip pressures is usually based upon estimated operating conditions for the most commonly used thicknesses and grades of medium and liner. However, when a box plant changes to paper specifications that yield machine operating conditions which deviate substantially from normal estimates, machine speeds often have to be reduced because the nip pressures are not optimum for the particular grades of paper being run through the machine. Moreover, if the medium is less than the full width of the machine, nip pressures must ordinarily be reduced to avoid metal to metal contact and possible damage to the ends of the corrugating rolls.
A further problem associated with conventional single facer machines relates to the damage sometimes caused by foreign objects carried into and through the nip of one or more of the rolls. Such damage can occur because of the large mass of the rolls, as well as the associated nip pressures applied to the rolls during the medium flute forming and liner applications processes. Typically, a point load will occur when a foreign object such as a tool goes through the nip center line defined by and extending between adjacent rolls. This point load will either require movement of the rolls to accomodate the dimensions of the foreign object, or deformation of the rolls, resulting in bending or breaking of roll flutes. However, the large mass and high loading of conventional rolls typically prevents such roll movement, so that flute damage is usually the result. Such conventional rolls are expensive to machine or replace, so that roll repair and/or replacement due to such damage can be a costly event.
An additional disadvantage associated with such conventional machines relates to the general operative environment surrounding them. As is well known, conventional corrugating machines create a high level of machine noise and vibration, and ear protection is thus usually required during machine operation. The noise and vibration in such machines is discreet in frequency, and the primary sources are traceable to the interactions between the upper and lower corrugating rolls, and to the interactions between the lower corrugating roll and the pressure roll. One source of such noise and vibration is traceable to machine forces which cause the lower corrugating roll to deflect in the direction of the pressure roll, resulting in impacts between the flutes of the lower corrugating roll and the pressure roll. Another source of noise and vibration is the medium flute forming process, which is effected in conventional machines simultaneously across the entire width of the medium. Attempts have been made to reduce such noise by providing corrugating rolls having curved flutes or rolls which are skewed relative to one another, to effect a non-simultaneous formation of flutes across the width of the medium. However, such designs add to machine complexity and/or roll machining occurs, or produce a non-standard product, and do nothing to reduce the above-noted problem of substantial roll mass and adaptability of such machines to different medium requirements.
A further problem associated with conventional single facer machines relates to uneven roll wear patterns created by the flute forming process. More particularly, over a period of time, the corrugating and pressure rolls will exhibit wear because the paper run through the machine is abrasive in nature. Yet the paper will vary in width in most box plants, and the average medium width will typically be less than the full width of the rolls. Roll wear will occur only where the medium runs through the machine, so that the corrugating and pressure rolls will typically exhibit a reduction in diameter generally in their middle zones under typical operating conditions, and suffer little diameter reduction at their longitudinal ends. When diameter reduction in the middle zone of the rolls exceeds the compressed thickness of typical paper medium (generally around 0.006 inches), metal to metal interference contact can occur between the corrugating rolls, with attendant damage to their flutes. Such mechanical interference also has the effect of reducing the nip pressure in the middle zone of the rolls, which can result in inadequate load for proper forming of flutes in the medium. Moreover, uneven wear of the lower corrugating roll and the pressure roll will eventually result in similar metal to metal contact between these two rolls near their longitudinal ends. Such contact tends to deform and damage the tips of the flutes of the lower corrugating roll.
In addition to the above, the efficient operation of single facer machines requires that the location of the rolls relative to one another be maintained to within relatively close tolerances. Thus, for example, it is desirable to locate and maintain the pressure roll so that it just kisses the lower corrugating roll. Moreover, machine noise and vibration, as well as roll wearing, are best reduced if the pressure roll can be located by way of a mechanical stop, rather than by biasing it against the lower corrugating roll. However, under operating conditions, nip loading of the upper corrugating roll tends to deflect the lower corrugating roll into the pressure roll. While the pressure roll is generally pre-ground with a negative crown to attempt to match the most likely machine operating conditions and roll deflections, the use of mechanical stops is very difficult, if not impossible, in conventional machines because several operating factors, such as roll loading, vibration, medium basis weight and width, roll thermal expansion, and roll wear, affect the actual shape of the roll and the amount of roll deflection in any particular operative situation.
As corrugating machine widths and speeds have increased in recent years, the problems of noise and vibration have also increased. It has been found that some conventional machines possess a resonant frequency falling within operating speed ranges of the machine. Thus, when the machine operates anywhere near its resonant frequency, severe increases in vibration and noise levels are observed. In such resonant ranges, these corrugating machines are more highly stressed and the likelihood of mechanical damage or structural failure is increased. Related to the above problem is the fact that machine vibrations created by the corrugating and pressure rolls cause or result in bearing loads which are far more significant than those associated with supporting a smoothly running system. As a result, the bearings and pivots in such conventional machines must be capable of withstanding significantly higher forces than they would otherwise experience in the absence of such vibration. This vibration loading in conventional corrugating machines generally requires high capacity bearings, sometimes of a particular or special design.
For these reasons, increased machine widths have encouraged the use of larger diameter corrugating rolls to provide additional rigidity, and to increase the stiffness and resonant frequency of the machine. However, such larger diameter corrugating rolls are disadvantageous for easy flute forming. The flute forming process in such machines requires the paper medium to be folded and gathered as it moves to the nip center line of the corrugating rolls. Typically, larger diameter corrugating rolls have a more complex labyrinth or "paper path", which can cause high tensions in the medium and result in medium fracturing. Moreover, large diameter corrugating rolls also have been found to operate optimally with large flute tip radii, which increases medium take-up ratio and resulting medium expense.
It is, therefore, desirable to provide a single facer corrugating machine which is more adaptable than prior known single facer corrugating machines to different operating conditions resulting from paper media of various weights, thicknesses and widths, and which can process diverse paper medium weights, thicknesses and widths without reducing machine operating speeds or operating the machine at reduced or non-preferred operating speeds and nip pressures. It is further desirable to provide such a single facer corrugating machine with reduced noise and vibration characteristics as compared with conventional single facer machines. It is also desirable to provide such a single facer corrugating machine which can more readily accommodate foreign objects such as tools which may enter the machine so as to reduce the possibility of roll and/or roll flute damage, as well as the equipment and labor costs associated with such events. It is further desirable to provide such a single facer corrugating machine which allows location of the corrugating and/or pressure roll assemblies by way of mechanical stops more readily than prior known single facer machines. It is also desirable to provide such a single facer corrugating machine which can accommodate roll wearing more readily than prior known machines, and which can be adjusted to compensate for uneven roll wear patterns attendant to machine operation with paper mediums of less than the full width of the machine roll assemblies. It is moreover desirable to provide such a single facer corrugating machine assembly which avoids the necessity of utilizing large diameter corrugating rolls and/or corrugating rolls with large flute tip radii so that operating expenses associated with increased roll cost, and increased medium take-up ratios and/or medium fracturing can be reduced and/or avoided. It is further desirable to provide such a single facer corrugating machine which avoids the necessity of utilizing special or high capacity bearings and pivots so that overall machine manufacturing costs can be reduced.
The present invention is intended to satisfy the above desirable features and objectives through the provision of a new and improved single facer corrugating machine having an elongated fluted lower corrugating roller and a series of fluted roll segments independently supported adjacent the lower corrugating roller at individual stations spaced along the length of the lower corrugating roller and which cooperate therewith to form corrugations in a paper medium passed therebetween. Each of the individual fluted roll segments is supported for rotation about its own discrete axis, and can be nip loaded against the lower corrugating roll independently of the other fluted roll segments. The invention also includes a pressure roll assembly for facilitating application of a liner to the corrugated medium comprised of individual pressure roll segments independently supported at stations spaced along the length of the lower corrugating roll. Each of the pressure roll segments is also supported for rotation about its own distinct axis, and can be nip loaded against the lower corrugating roll independently of the other pressure roll segments. Each of the fluted roll segments and pressure roll segments is positionable relative to the lower corrugating roll independently of its other associated roll segments to facilitate phase control across the width of the machine, and in the machine direction, of roll interactions associated with corrugation formation and liner application for the purpose of controlling and reducing overall machine noise and vibration. Independent stops are also provided for each of the roll segments to allow the mechanical location of the roll segments relative to the lower corrugating roller. Provision is also made for adjusting the parallelism of each roll segment relative to the lower corrugating roll.
The individual roll segment design of the invention also allows for independent positioning of particular roll segments to compensate for uneven roll wear, and independent adjustment of nip loading to optimize operating conditions for paper mediums of diverse widths and thicknesses. The segmented roll design of the invention also yields a machine which avoids the problem of large roller mass, since any individual roll segment can more readily accommodate foreign objects which may find their way into the machine. Moreover, the segmented roll design eliminates the need for special or high capacity bearings and pivots of the type associated with conventional roll assemblies of substantial mass.